Method and apparatus for applying a halogenatedhydrocarbon solventcontaining enamel to wire



Aug. 29, 1967 O H LINDEMANN METHOD AND APPARATUS F OR APPLYING A HALOGENATED HYDROCARBON Filed Aug. 6, 1963 SOLVENT-CONTAINING ENAMEL TO WIRE 2 Sheets-Sheet 1 Aug. 29. 1967 o. H. LINDEMANN 3,333,733

METHOD AND APPARATUS FOR APPLYING A HALOGENATED HYDROCARBON SOLVENT-CONTAINING ENAMEL TO WIRE Filed Aug. 6, 1963 2 Sheets-Sheet 2 United States Patent. OfiFice 3,338,738 Patented Aug. 29, 1967 3,338,738 METHOD AND APPARATUS FOR APPLYING A HALOGENATEDHYDROCARBON SOLVENT- CONTAINING ENAMEL T WIRE Otto H. Lindemann, Buffalo, N.Y., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York Filed Aug. 6, 1963, Ser. No. 300,320 14 Claims. (Cl. 117-102) This invention relates to wire-enameling apparatus and is particularly concerned with apparatus of the character mentioned which is intended for use with coating compositions held at elevated temperatures.

It is an object of the present invention to provide novel apparatus by which wire-enameling with hot, substantially non-flammable volatile solvent-based, coating compositions can be conveniently and economically carried out.

Another object of the invention is to provide novel apparatus of the character described which is simple and inexpensive to construct.

Still another object of the invention is to provide a satisfactory process for enameling wire with hot, substantially non-flammable volatile solvent-based, coating compositions.

Other objects and advantages of the invention will be apparent from the following description thereof taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a vertical sectional view of apparatus according to the invention;

FIGURE 2 is a sectional view taken on line 22 of FIGURE 1 of the coating tank shown in FIGURE 1; and

FIGURE 3 is a top plan View of the coating tank shown in FIGURE 2.

Hitherto no apparatus has been available for efficient wire enameling with hot liquid coating compositions which include substantial quantities of volatile, non-flammable, solvents, preferably halogenated hydrocarbon solvents such as trichloroethylene, perchloroethylene, carbon tetrachloride, and the like and which are generally maintained during use at temperatures below the boiling points of the solvents. The apparatus of the present invention makes possible the continuous application to a wire of a succession of films of enamel and the necessary baking of the several films while at the same time avoiding loss of the expensive volatile solvent.

Since the compositions used for hot-dip wire enameling in general tend to be somewhat thermally unstable it is contemplated that the coating bath shall occupy a relatively small volume. This has the additional advantage that it facilitates the maintenance of the proper proportions of ingredients in the composition in the coating bath.

In accordance with the present invention, the subject process for coating wire comprises passing a wire to be coated through a halogenated hydrocarbon vapor zone into a hot coating composition comprised of film forming ingredients and a halogenated hydrocarbon solvent for at least the major portion of the film-forming ingredients,

said coating composition being at a temperature below the boiling point of the solvent, removing the wire from the coating composition and again passing it through the halogenated hydrocarbon vapor zone, repeating the above procedure so as to form on the wire successive films of the coating composition and subjecting the wire to heating between successive passages through the coating composition, thereby reducing the solubility of the film of coating compositions on the wire.

Referring more specifically to the drawings, the numeral 11 designates a coating tank which is substantially rectangular in shape at its upper end and is adapted to hold a liquid coating composition bath 9. The tank 11 comprises an elongated, trough-like body 12 of U-shaped cross section having ends 13 and 14. Around the upper end of the tank 11 and extending outwardly and upwardly therefrom is a rectangular enclosure 16 which comprises sides 17 and 18 and ends 19 and 20.

At the bottom of the enclosure 16, a flange or rim 22 projects inwardly from the sides and ends thereof and is attached to the tank 11 below the upper extremities of the body 12 and the ends 13 and 14, whereby to form a peripheral trough 23 around the upper edges of the tank 11. The trough 23 is provided to catch solvent condensed on the cooling coils 24 which are suspended by any suitable means and extend around the inner periphery of the base of the enclosure 16. A peripheral cooling jacket 25, containing a coolant 8 is provided around the exterior of the base of the enclosure 16 and under the flange or rim 22. Thus, the jacket may serve to cool the contents of the trough 23. It is desirable that the solvents condensing and collecting means, which includes the coils 24, the jacket 25 and the trough 23, be positioned in the coating section of the apparatus in such a manner that only a relatively small vapor zone is formed between the upper surface of the coating composition 9 in the tank 11 and the lowermost cooling coil 24. Often, it has been found that good results are obtained when the height of the vapor zone is not greatly in excess of about 3 to 4 inches, although under some operating conditions appreciably larger vapor zones, e.g., 10 to 15 inches, may be used and still yield acceptable results. Generally, it is desirable that the vapor Zone not be of such size that appreciable vapor washing of coating on the product takes place under the operating conditions used.

Rotatably supported in bearings 27 in the tank 11 is a coating drum or roll 28 which is provided with a plurality of longitudinally spaced, peripheral grooves 29 adapted to receive the wire 30. Preferably, the diameter of the drum 28 is relatively large with respect to the width of the tank 11, so that the volume of the coating bath will be relatively small.

Spaced from and above the coating tank 11 is a drying of curing section designated generaly by the numeral 32 and suitably supported by means not shown. The curing section 32 may be of any suitable configuration, but conveniently may be a rectangular box-like structure having an open side which is directed downwardly approximately vertically over the coating tank 11. Within the curing section there are provided spaced bearings 34 for supporting a roll or drum 35 which is preferably parallel with the drum 28. The roll 35 is provided with a plurality of longitudinally spaced, peripheral grooves 36 which are preferably aligned with grooves 29 on the drum 28. Around the interior walls of the lower portion of the section 32 are a plurality of heat lamps 38, suitably connected to a supply of electrical current by means not shown. There is thus provided an oven portion 39 by means of which the wire 30 may be heated.

In using the apparatus described above, the Wire 30 is fed around the drums 28 and 35 from a rotatably supported supply reel (not shown), the leading end 30a of the wire being secured to a take-up reel (not shown) which may be driven by any suitable means to pull the Wire through the apparatus. The Wire is held against endwise movement on the drums by the aligned grooves 29 and 36, and the drums, as well as the supply reel, are freely rotatable. The tank 11 is then filled with the hot, liquid coating composition to form a coating bath 9, the cooling coil 24 is connected by pipes 40 and 41 to a suitable source of coolant (not shown), and the jacket 25 is also connected by pipes 42 and 43 to a suitable source of coolant (not shown). When the heat lamps 38 in the oven portion 39 are supplied with electrical energy the apparatus is ready for use and the take-up reel (not shown) may be rotated to pull the wire 30 through the system.

As will be apparent, the bare wire 30 entering the apparatus is heated in the oven portion 39 and then passes downwardly through the vapor zone formed between the cooling coils 24 and the upper surface of the coating composition into the coating bath 9. As the wire emerges from the bath and passes back through the vapor zone, a substantial portion of the volatile solvent in the coating composition flashes ofi from the film of coating composition on the wire since its vapor pressure is quite high at the temperature of the bath. After passing through the vapor zone, the coated wire passes through the zone between the coating section and the curing section of the apparatus. In this area, generally, substantially all of the the solvent in the film of coating composition, which was not flashed off in passing through the vapor zone, is removed before the wire comes into the curing section. This solvent removal area may be open to the atmosphere, as shown in the drawing. If desired, it may be enclosed and may contain air, or some other gas which is non-reactive or is not objectionably reactive with the coated wire, e.g., nitrogen. In some instances it may be under vacuum. The wire carrying the residual, substantially dry and solventfree film then passes into the curing section 32 and over the drum 35 and while in the oven 39 is baked sufliciently to substantially insolubilize the film thereon. Because little, if any, solvent is left to be driven off from the film in the oven 39, there is substantially no surface deformation of the film as would normally be caused by the rapid release of large amounts of solvent in this zone. Accordingly, when the wire leaves the oven and again runs through the coating bath, around the drum 28, the film already on the wire is substantially continuous and is not dissolved but another film is deposited on the previously applied one.

The wire is repeatedly passed around the drums 28 and 35 so that a succession of insoluble films of enamel or the like is applied thereon until the coating is of the thickness desired. The number of passages through the bath is determined by the number of times the wire passes around the drum 28. Preferably, a separate groove 29 is provided on the drum for each such passage.

Obviously, the coating material in the tank 11 will change in composition over a period of time because of evaporation of solvent. It is therefore preferred to circulate the coating material continuously during operation of the apparatus. The proportions of the ingredients in the coating composition may thus be maintained constant, new ingredients being added as required. It will be seen that the relatively small volume of the coating bath will rsult in the complete renewal of the bath at frequent intervals as it is used and new ingredients are added.

In FIGURE 2, the general design of the circulatory equipment and connections employed are shown schematically. Hot coating material of the desired composition is supplied to the tank 11, adjacent the top thereof, through the line 45, passing through the inlet 59 in the insulation 58 and the trough body 12. At the bottom of the tank 11 is a valved drain line 416 which passes through the outlet 6%) in the trough body 12 and the insulation 58 and runs to a pump 47 that circulates the coating material withdrawn from the tank through a filter 48 and a heater 49 to the line 45. The solvent which evaporates from the surface of the coating bath, and from the films of coating material on the wire 30, condenses on the coil 24 and drips into the trough 23 from which it is withdrawn through the line 54), passing through the outlet 61 in the trough 23 and the outlet 62 in the cooling jacket 25, and is led to a separator 51. In the separator the solvent, being heavier than water, settles out of the associated condensed Water vapor. The latter is led by the line 52 to waste, while the solvent is returned to the inlet of pump 47 through the line 53. In order to control and adjust the composition of the coating material, solvent may be withdrawn from the system through the valved line 54 and additional film-forming ingredients may be admitted through the valved line 55 which connects to line 46.

It must be kept in mind when considering the apparatus and the wire-enameling process described herein that the apparatus is particularly designed for efiicient operation with a process that involves the use of hot, liquid coating compositions which comprise film-forming ingredients and, as a solvent for at least the major portion of said ingredients, a relatively heavy, low-boiling, substantially non-flammable, halogenated hydrocarbon solvent such as trichloroethylene, carbon tetrachloride, perchloroethylene, the trichloroethanes, the tetrachloroethanes, methylene chloride, ethylene dichloride, ethylidene chloride, the dichlorotetrafluoroethanes, the trichlorotrifiuoroethanes, the trichlorodifluoroethanes, the tetrachlorodifiuoroethanes, the fluorotrichloroethanes, the fluorotetrachloroethanes, methyltrichloroethylene, 1,2-dichloropropane, 1,2-dichloropropene, 1,1,2-trichloropropane. ethyltrichloroethylene, mixtures thereof, as well as other halogen analogs of the above. As will be noted, these materials are generally of about 1 to 4 carbon atoms and about 1 to 6 halogen atoms. Of these, the preferred material is trichloroethylene. It is also to be remembered that for most efficient results a coating composition of the type described should be maintained at a temperature which is not greatly lower than that at which the solvent boils.

In the use of the novel apparatus of the invention, the material used for the enamel coating on the wire is not critical. Various suitable compositions with or without pigments are well-known and many are commercially available. Accordingly, there is no need for specifically setting forth here the formula of any particular composition. Suffice it to say that alkyd resins, phenolic resins, epoxy resins, polyurethane resins and the like are examples of the resins which may be used. The temperature at which the coating bath is maintained will vary according to the composition thereof and particularly in accordance with the specific solvent employed. For example, in some instances, temperatures which are 40-50 degrees centigrade below the boiling point of the solvent may be used. In general, it is preferred to maintain the composition at a temperature only slightly below the boiling point of the solvent used, e.g., 2-25 degrees centigrade. Thus, when using a coating composition based on trichloroethylene as a solvent, the coating material will preferably be heated by the heater 49 to such a temperature as will maintain the bath at about 70-80 degrees centigrade. A layer of insulation 58 may be provided around the tank 11 to assist in keeping the temperature of the bath constant.

Important in achieving the highly eflicient operation of the apparatus of the present invention are the building up of a coating layer of desired thickness by successive passages of the wire through the same coating bath, the use of a coating bath of relatively small volume, whereby the composition and temperature of the bath may be better controlled and maintained constant, and the use of highly eflicient condensation means for the volatile solvent.

The first two of the points mentioned above permit economy of space as well as equipment since a plurality of coating tanks are not necessary and the single tank used need be only slightly larger than the drum 28. The third point referred to is the positioning of the solvent condensing and collecting means in the coating section of the apparatus so as to form the relatively small vapor zone referred to hereinabove. This small vapor zone is desirable in that there is a smoothing or leveling of the coating on the wire as it passes out of the coating bath and through this zone, without excessive removal of the coating film. Additionally, in passing downwardly through this vapor zone into the coating bath, after passing through the curing section, a conditioning of the coated wire surface may be considered to take place to make it more receptive to the next layer of coating. This conditioning may be the result of a slight swelling of the outermost portion of the coating by the solvent vapors in the vapor zone. To further illustrate the advantages of the present process, conventional wire enameling, as generally practiced at present, takes place at room temperature. That is, the paint is at room temperature. Secondly, ordinary wire enamel contains a blend of an aliphatic solvent with an aromatic solvent whereby the KB value (a measure of solvency) is less than 80.

The present trichlor enameling process takes into account the high solvency of the trichloroethylene (about KB 133) and the relatively high temperature of application viz. circa 180 degrees Fahrenheit. It is well known that paint adheres poorly (in most cases) to smooth, baked enamel surfaces and every advantage is needed to improve this adherence. The high solvency of the trichlor in the trichlor enamel and the high temperature of application tend to soften and swell the baked-on enamel. At the same time, the elevated temperature increases the wetting power of the paint being applied.

The vapor zone above the liquid paint allows a faster movement of the wire through the paint because more time is allowed for free leveling before setting of the paint takes place.

It will be appreciated that although the present apparatus has been described in its most preferred embodiment as having the solvent collecting trough 23 positioned laterally outwardly from the tank 11, this trough may be formed so as to be within the tank, if desired. Also, it will be understood that there are other possible variations in the process and apparatus herein disclosed so that numerous modifications in the apparatus shown may be made without departing from the spirit of the present invention. For example, while the apparatus is preferably formed of metal, the kind of metal may vary. Additionally, of course, the size of the apparatus including the number of grooves in the drums 28 and 35 may be varied as desired, and so may be the shapes and arrangements of various components. Moreover, the apparatus and process of the present invention may be used with substantially non-flammable solvents other than the halogenated hydrocarbons with comparable results. Accordingly, it is to be understood that it is intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. A process for coating a wire which consists essentially of passing a wire through a halogenated hydrocarbon vapor zone into a hot coating composition comprised of film-forming ingredients and a halogenated hydrocarbon solvent for at least the major portion of the fihnforming ingredients, said coating composition being at a .temperature below the'boiling point of the solvent, re- -moving the wire from the coating composition, effecting leveling and smoothing of the thus-deposited film of coating composition by, again passing it through the halogenated hydrocarbon vapor zone, said vapor zone being of a size such that substantially no vapor washing of the film of coating composition takes place, repeating the above procedure so as to form on the wire successive films of the coating composition and subjecting the wire to heating between successive passages through the coating composition, thereby reducing the solubility of the film of coating composition on the wire.

2. A process as claimed in claim 1 wherein the wire is heated before its initial passage through the coating composition.

3. A process as claimed in claim 2 wherein the temperature of the coating composition is within the range of about 2 to about 25 degrees centigrade below the boiling point of the solvent.

4. A process as claimed in claim 2 wherein the coated wire is passed through a solvent removal zone after passing through the solvent vapor zone and before being reheated, whereby substantially all of the solvent in the film coating, not removed in passing through the vapor zone, is removed before the coated wire passes into the heating zone.

5. A process as claimed in claim 4 in which coating composition is continuously withdrawn from said bath and additional hot coating composition is fed to said bath.

6. A process as claimed in claim 5 in which the solvent vapor in the solvent vapor zone is condensed and recovered.

7. Wire coating apparatus for use with hot coating compositions that include film-forming ingredients and a halogenated hydrocarbon solvent for at least the major portion of the film-forming ingredients, said coating composition being used at a temperature below the boiling point of the solvent, which consists essentially of, a coating section and a curing section, the coating section consisting essentially of a container adapted to hold the hot coating composition, solvent condensing and collecting means positioned in the coating section so as to form a relatively small halogenated hydrocarbon solvent vapor zone immediately above the surface of the coating composition in the container, said vapor zone being of a size such that substantially no vapor washing of the film of coating composition on the wire takes place and means for repeatedly passing a wire through the coating composition, so as to pass through the solvent vapor zone, both before and after passing through the coating composition, and the curing section consisting essentially of means adapted to heat the wire between passages thereof through the coating composition.

8. Apparatus as claimed in claim 7 wherein the solvent condensing and collecting means consists essentially of a cooling coil around the upper portion of the container, above the level of the coating composition, a trough positioned below the cooling coils and adapted to collect condensed solvent vapor and a cooling jacket surrounding at least a portion of the underside of the trough.

9. Apparatus as claimed in claim 8 wherein the curing section of the apparatus is spaced apart from the coating section.

10. Apparatus as claimed in claim 9 wherein the area between the coating and curing sections of the apparatus is sufiicient to provide a solvent removal zone wherein substantially all of the solvent remaining in the coating composition on the wire, after passage through the vapor zone, is removed prior to passing into the heated portion of the curing section.

11. Apparatus as claimed in claim 10 in which the means for repeatedly passing the wire through the coating composition is a rotatably supported drum, positioned within the container.

7 12. Apparatus as claimed in claim 11 in which the coating container is a tank which is substantially rectangular at its top.

13. Apparatus as claimed in claim 12 in which the 'rotatably supported drum in the tank has a diameter which is relatively large with respect to the width of said coating tank.

14. Apparatus as claimed in claim 13 in which means is provided for withdrawing coating composition from said References Cited UNITED STATES PATENTS Fruth 117-115 X Borushko. 1'17-102 Saums et al. 118-420 X Hendrixson 117-102 X Randall et a1 134-105 X Pokorny 117-102 X tank and for supplying hot coating composition to said 10 ALFRED LEAVITT, Primary Examiner- J. R. BATTEN, JR., Assistant Examiner.

tank. 

1. A PROCESS FOR COATING A WIRE WHICH CONSISTS ESSENTIALLY OF PASSING A WIRE THROUGH A HALOGENATED HYDROCARBON VAPOR ZONE INTO A HOT COATING COMPOSITION COMPRISED OF FILM-FORMING INGREDIENTS AND A HALOGENATED HYDROCARBON SOLVENT FOR AT LEAST THE MAJOR PORTION OF THE FILMFORMING INGREDIENTS, SAID COATING COMPOSITION BEING AT A TEMPERATURE BELOW THE BOILING POINT OF THE SOLVENT, REMOVING THE WIRE FROM THE COATING COMPOSITION, EFFECTING LEVELING AND SMOOTHING OF THE THUS-DEPOSITED FILM OF COATING COMPOSITION BY AGAIN PASSING IT THROUGH THE HALOGENATED HYDROCARBON VAPOR ZONE, SAID VAPOR ZONE BEING OF A SIZE SUCH THAT SUBSTANTIALLY NO VAPOR WASHING OF THE FILM OF COATING COMPOSITION TAKES PLACE, REPEATING THE ABOVE PROCEDURE SO AS TO FORM ON THE WIRE SUCCESSIVE FILMS OF THE COATING COMPOSITION AND SUBJECTING THE WIRE 